Given that the anti-science, pro-pollution forces seem to be succeeding in their fight to keep us on our current emissions path, it’s no surprise that multiple recent analyses conclude that we face a temperature rise that is far, far beyond dangerous:

There is a small group of self-proclaimed “lukewarmers” who don’t know the scientific literature well or are just outright anti-science disinformers. They assert, despite all the science to the contrary, that the sensitivity of the climate to fast feedbacks is very low. They then blindly ignore factors #2 and #3 above in order to claim total warming this century will be maybe 1°C — or 2°C at most — no big deal, according to this dangerously confused and/or misguided group.

Note: Everything that follows is from Skeptical Science, until the italicized line beginning with my initials, JR.

Some global warming ‘skeptics’ argue that the Earth’s climate sensitivity is so low that a doubling of atmospheric CO2 will result in a surface temperature change on the order of 1°C or less, and that therefore global warming is nothing to worry about. However, values this low are inconsistent with numerous studies using a wide variety of methods, including (i) paleoclimate data, (ii) recent empirical data, and (iii) generally accepted climate models.

Climate sensitivity describes how sensitive the global climate is to a change in the amount of energy reaching the Earth’s surface and lower atmosphere (a.k.a. a radiative forcing). For example, we know that if the amount of carbon dioxide (CO2) in the Earth’s atmosphere doubles from the pre-industrial level of 280 parts per million by volume (ppmv) to 560 ppmv, this will cause an energy imbalance by trapping more outgoing thermal radiation in the atmosphere, enough to directly warm the surface approximately 1.2°C. However, this doesn’t account for feedbacks, for example ice melting and making the planet less reflective, and the warmer atmosphere holding more water vapor (another greenhouse gas).

Climate sensitivity is the amount the planet will warm when accounting for the various feedbacks affecting the global climate. The relevant formula is:

dT = Î»*dF

Where ‘dT’ is the change in the Earth’s average surface temperature, ‘Î»’ is the climate sensitivity, usually with units in Kelvin or degrees Celsius per Watts per square meter (°C/[W m-2]), and ‘dF’ is the radiative forcing, which is discussed in further detail in the Advanced rebuttal to the ‘CO2 effect is weak’ argument.

Climate sensitivity is not specific to CO2

A common misconception is that the climate sensitivity and temperature change in response to increasing CO2 differs from the sensitivity to other radiative forcings, such as a change in solar irradiance. This, however, is not the case. The surface temperature change is proportional to the sensitivity and radiative forcing (in W m-2), regardless of the source of the energy imbalance.

In other words, if you argue that the Earth has a low climate sensitivity to CO2, you are also arguing for a low climate sensitivity to other influences such as solar irradiance, orbital changes, and volcanic emissions. Thus when arguing for low climate sensitivity, it becomes difficult to explain past climate changes. For example, between glacial and interglacial periods, the planet’s average temperature changes on the order of 6°C (more like 8-10°C in the Antarctic). If the climate sensitivity is low, for example due to increasing low-lying cloud cover reflecting more sunlight as a response to global warming, then how can these large past climate changes be explained?

Figure 1: Antarctic temperature changes over the past 450,000 years as measured from ice cores

What is the possible range of climate sensitivity?

The IPCC Fourth Assessment Report summarized climate sensitivity as “likely to be in the range 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values.”

Individual studies have put climate sensitivity from a doubling of CO2 at anywhere between 0.5°C and 10°C; however, as a consequence of increasingly better data, it appears that the extreme higher and lower values are very unlikely. In fact, as climate science has developed and advanced over time , estimates have converged around 3°C. A summary of recent climate sensitivity studies can be found here.

A study led by Stefan Rahmstorf concluded “many vastly improved models have been developed by a number of climate research centers around the world. Current state-of-the-art climate models span a range of 2.6-4.1°C, most clustering around 3°C” (Rahmstorf 2008). Several studies have put the lower bound of climate sensitivity at about 1.5°C,on the other hand, several others have found that a sensitivity higher than 4.5°C can’t be ruled out.

A 2008 study led by James Hansen found that climate sensitivity to “fast feedback processes” is 3°C, but when accounting for longer-term feedbacks (such as ice sheet
disintegration, vegetation migration, and greenhouse gas release from soils, tundra or ocean), if atmospheric CO2 remains at the doubled level, the sensitivity increases to 6°C based on paleoclimatic (historical climate) data.

What are the limits on the climate sensitivity value?

Paleoclimate

The main limit on the sensitivity value is that it has to be consistent with paleoclimatic data. A sensitivity which is too low will be inconsistent with past climate changes – basically if there is some large negative feedback which makes the sensitivity too low, it would have prevented the planet from transitioning from ice ages to interglacial periods, for example. Similarly a high climate sensitivity would have caused more and larger past climate changes.

One recent study examining the Palaeocene-Eocene Thermal Maximum (about 55 million years ago), during which the planet warmed 5-9°C, found that “At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration, this rise in CO2 can explain only between 1 and 3.5°C of the warming inferred from proxy records” (Zeebe 2009). This suggests that climate sensitivity may be higher than we currently believe, but it likely isn’t lower.

Recent responses to large volcanic eruptions

Climate scientists have also attempted to estimate climate sensitivity based on the response to recent large volcanic eruptions, such as Mount Pinatubo in 1991. Wigley et al. (2005) found:

“Comparisons of observed and modeled coolings after the eruptions of Agung, El Chich³n, and Pinatubo give implied climate sensitivities that are consistent with the Intergovernmental Panel on Climate Change (IPCC) range of 1.5-4.5°C. The cooling associated with Pinatubo appears to require a sensitivity above the IPCC lower bound of 1.5°C, and none of the observed eruption responses rules out a sensitivity above 4.5°C.”

“A climate feedback parameter of 2.3 +/- 1.4 W m-2 K-1 is found. This corresponds to a 1.0-4.1 K range for the equilibrium warming due to a doubling of carbon dioxide”

Other Empirical Observations

Gregory et al. (2002) used observed interior-ocean temperature changes, surface temperature changes measured since 1860, and estimates of anthropogenic and natural radiative forcing of the climate system to estimate its climate sensitivity. They found:

Examining Past Temperature Projections

In 1988, NASA climate scientist Dr James Hansen produced a groundbreaking study in which he produced a global climate model that calculated future warming based on three different CO2 emissions scenarios labeled A, B, and C (Hansen 1988). Now, after more than 20 years, we are able to review Hansen’s projections.

Hansen’s model assumed a rather high climate sensitivity of 4.2°C for a doubling of CO2. His Scenario B has been the closest to reality, with the actual total radiative forcing being about 10% higher than in this emissions scenario. The warming trend predicted in this scenario from 1988 to 2010 was about 0.26°C per decade whereas the measured temperature increase over that period was approximately 0.18°C per decade, or about 40% lower than Scenario B.

Therefore, what Hansen’s models and the real-world observations tell us is that climate sensitivity is about 40% below 4.2°C, or once again, right around 3°C for a doubling of atmospheric CO2.

Probabilistic Estimate Analysis

Annan and Hargreaves (2009) investigated various probabilistic estimates of climate sensitivity, many of which suggested a “worryingly high probability” (greater than 5%) that the sensitivity is in excess of than 6°C for a doubling of CO2. Using a Bayesian statistical approach, this study concluded that

“the long fat tail that is characteristic of all recent estimates of climate sensitivity simply disappears, with an upper 95% probability limit…easily shown to lie close to 4°C, and certainly well below 6°C.”

Annan and Hargreaves concluded that the climate sensitivity to a doubling of atmospheric CO2 is probably close to 3°C, it may be higher, but it’s probably not much lower.

Figure 2: Probability distribution of climate sensitivity to a doubling of atmospheric CO2

Summary of these results

Knutti and Hegerl (2008) presents a comprehensive, concise overview of our scientific understanding of climate sensitivity. In their paper, they present a figure which neatly encapsulates how various methods of estimating climate sensitivity examining different time periods have yielded consistent results, as the studies described above show. As you can see, the various methodologies are generally consistent with the range of 2-4.5°C, with few methods leaving the possibility of lower values, but several unable to rule out higher values.

Figure 3: Distributions and ranges for climate sensitivity from different lines of evidence. The circle indicates the most likely value. The thin colored bars indicate very likely value (more than 90% probability). The thicker colored bars indicate likely values (more than 66% probability). Dashed lines indicate no robust constraint on an upper bound. The IPCC likely range (2 to 4.5°C) and most likely value (3°C) are indicated by the vertical grey bar and black line, respectively.

What does all this mean?

According to a recent MIT study, we’re currently on pace to reach this doubled atmospheric CO2 level by the mid-to-late 21st century.

Figure 4: Projected decadal mean concentrations of CO2. Red solid lines are median, 5%, and 95% for the MIT study, the dashed blue line is the same from the 2003 MIT projection.

So unless we change course, we’re looking at a rapid warming over the 21st century. Most climate scientists agree that a 2°C warming is the ‘danger limit’. Figure 5 shows temperature rise for a given CO2 level. The dark grey area indicates the climate sensitivity likely range of 2 to 4.5°C.

Figure 5: Relation between atmospheric CO2 concentration and key impacts associated with equilibrium global temperature increase. The most likely warming is indicated for climate sensitivity 3°C (black solid). The likely range (dark grey) is for the climate sensitivity range 2 to 4.5°C. Selected key impacts (some delayed) for several sectors and different temperatures are indicated in the top part of the figure.If we manage to stabilize CO2 levels at 450 ppmv (the atmospheric CO2 concentration as of 2010 is about 390 ppmv), according to the best estimate, we have a probability of less than 50% of meeting the 2°C target. The key impacts associated with 2°C warming can be seen at the top of Figure 5. The tight constraint on the lower limit of climate sensitivity indicates we’re looking down the barrel of significant warming in future decades.

“Global warming of 2°C would leave the Earth warmer than it has been in millions of years, a disruption of climate conditions that have been stable for longer than the history of human agriculture. Given the drought that already afflicts Australia, the crumbling of the sea ice in the Arctic, and the increasing storm damage after only 0.8°C of warming so far, calling 2°C a danger limit seems to us pretty cavalier.”

– Posted by dana1981 at 10:35 AM

JR: A number of major studies looking at paleoclimate data come to the same conclusion. Here are three:

Scientists analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature (subs. req’d), found Artic temperatures almost beyond imagination-above 23°C (74°F)-temperatures more than 18°F warmer than current climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.

A second study, published in Geophysical Research Letters(subs. req’d), looked at temperature and atmospheric changes during the Middle Ages. This 2006 study found that the effect of amplifying feedbacks in the climate system-where global warming boosts atmospheric CO2 levels-“will promote warming by an extra 15 percent to 78 percent on a century-scale” compared to typical estimates by the U.N.’s Intergovernmental Panel on Climate Change. The study notes these results may even be “conservative” because they ignore other greenhouse gases such as methane, whose levels will likely be boosted as temperatures warm.

The third study, published in Geophysical Research Letters (subs. req’d), looked at temperature and atmospheric changes during the past 400,000 years. This study found evidence for significant increases in both CO2 and methane (CH4) levels as temperatures rise. The conclusion: If our current climate models correctly accounted for such “missing feedbacks,” then “we would be predicting a significantly greater increase in global warming than is currently forecast over the next century and beyond”-as much as 1.5°C warmer this century alone.

What are these “missing feedbacks” in the global carbon cycle?

The best evidence is that the climate is now being driven by amplifying feedbacks “” see, most notably:

It is also worth pointing out that it is possible that climate sensitivity is on the high side (or that amplifying feedbacks are on the high side). If so, we risk very high warming much faster than virtually anyone realizes:

Bottom Line: The “lukewarmer” assertion that climate impacts this century are likely to be insignificant or mild is a dangerous delusion that is based on wishful thinking (or intentional disinformation), not science.

66 Responses to A detailed look at climate sensitivity

Been commenting awhile on this latest trend towards lukewarming. Expect to see further variants of the same on the political scene is my prediction. It’s opened up a second front on science: though some of the diehards seem disappointed that their erstwhile leading lights no longer crow “It’s all a hoax”, they continue to carry on crowing whilst their heroes project themselves as a little more reasonable – a stance that folds as soon as one picks apart what they are saying. So we have opposition on two levels of opinionology (or obfuscatology?) now!

John Cook is doing a sterling service in the context of presenting the science itself – the important bit in all of this – in an objective and sober way. His approach should be an inspiration to all workers in the field of climate change.

Forecast to be 95 today in my part of the world. Usually late Sept. is in the 80s, if that. Has been going on all month, unusually high temps. Can see smoke from an out of control wildfire that’s now at 22,000 acres. The tomatoes in friends’ gardens didn’t work out this year because of an unusual blight of some kind.

I’m beginning to wonder what the future holds. I used to think I wouldn’t be much affected by global warming, I’m no kid and I figured I’d be long gone by the time its effects were felt. I still felt a need to try to reduce pollutants, I care about the other critters on this planet.

Now I’m not so sure that I won’t see it all come crashing down. Those who are stymying efforts to cut pollutants back are criminals, I hope their feet are held to the fire when the SHTF. The wealthy may think they can hide from it in their rich enclaves, but nature has no respect for money.

I think it could be more effective to consistently phrase the climate impacts as “what kids today will experience” rather than a year like 2100.

For example when I read “MIT doubles its 2095 warming projection to 10F”, I think that is ugly a long time from now. But when I realize the kid walking down the street right now will face that, it changes how I process it and the imperative I give it.

EO WIlson in his book “Future of Life” talks about the evolutionary imprint on humans that causes us to put a very high priority on things that effect our local clan and our kids. Conversely humans tend to highly discount events outside this sphere and timeframe. But now climate is entering that realm and timeframe.

I’m very thankful for all your work, Joe, at Climate Progress to focus climate impacts on just this reality of “it is happening now and will hammer your kids”. The denial machine likewise goes ape over anything that brings climate impacts into this clan/kids frame as they know that it is game over for delay once that link is made for most humans.

If it comes slowly, we can adapt to climate change, it is sudden changes that wreck our infrastructure, spoil agriculture, and flood the land. Such events are by definition, weather.

Changing climate conditions give us more intense weather, and as climate changes much faster than the models predicted, weather will be more intense than any scenario considered by the IPCC.

Last summer’s Russian heat wave and Pakistan flood was driven (in part) by heat and water vapor in the Arctic that helped “block” the jet stream.” Nothing in AR4 hinted that climate change would be rapid enough to allow the Arctic to supply heat and water vapor to weather events in 2010.

The European heat wave, the Russian heat wave, the Pakistan floods, and the 2009 Atlantic coast snow events were driven (in part) by a 0.6C to 0.7C degree rise in global energy. And, it is worth noting how unpredictable these events are. At rise in global energy of 1.2C we are taking about twice as much change in heat heat to drive weather events that are twice as much larger and twice as much more intense. How big? Bigger than the last storm to pass over New Zealand.

Moreover, when Greenland has sources of water vapor, we open the door to ice collapse events as calculated by Feynman. (Greenland is now getting water vapor.) Then, sea level rise can occur fast enough to be weather.

Anything is cheaper than the infrastructure damage that weather events resulting from the rapid addition of another 100 ppmv CO2 to the atmosphere would cause. Anything. For example after you lose agricultural infrastructure, most people starve to death.

The knee-jerk reaction of large governments to huge weather disasters will be the government nationalizing remaining resources. If the conservatives want to avoid this (socialism), they need to get on board to rapidly slow CO2 and CH4 emissions.

Thanks to both you and John Cook, whose website has been a treasure for a while now. John also did an excellent illustrated summary of the terrestrial carbon cycle.

Ominous Clouds Overhead: Have you ever hung around members of the extremely wealthy far right? I confess to finding myself in their company from time to time. People don’t realize that characters like David Koch and Don Blankenship are quite crazy, even if they privately give some credence to climate science. They believe that their money will insulate them and their descendants through relocation to private fortresses in northern latitudes, protected from desperate refugees by mercenaries. It’s not so different from the way they live in their gated communities now. They are truly unconcerned about the rabble.

Their science is wrong here, too. Even today an infrantryman can take out fixed fortifications.

The diseased economic organism spreading philosophically unabated globally operates under the cultural myth of western thought which perversely defines three states of buried matter (carbon) as “energy resources.”

Pay no attention to policies of nation-state power which arrange for numerous climate change encouragements by monetizing minerals, providing unaccounted $ trillions in annual direct, indirect and “externalized” subsidies for “fuels,” along with other foreign and domestic policies of destruction.

A civilization based on myth will collapse (one way or another). What is that I heard about an energy revolution? Oh yes, that was last century.

For me, this is the best kind of post you (and, of course, Skeptical Science) do. I find the “advanced” explanations to be easily followed and yet informative enough that I (as a physical-inorganic chemist) get a lot that is useful out of it. Well done.

Mike, I used to live in Aspen, and I also have wealthy Alaskan relatives who support Palin (not monetarily, AFAIK, but in theory). Right-wing religious types. Enough said.

You’re very right. They’re all truly delusional. They may be good at making money, but they’re not very bright when it comes to the long-term view—and most of them seriously underestimate their fellow humans and overestimate what you can buy with money.

Joe: I agree with others here — this is easily one of your best posts, which is saying a lot.

We’ve seen a long list of “it’s worse than we thought” discoveries in the last couple of years, which convinces me that we’re still cognitively behind the curve. This is a very bad situation; the normal and wholly appropriate caution of the scientific process is just another weight we’re dragging, along with inadequate funding and other self-imposed issues, as we try to catch up to reality.

John: I agree — we will see a continued trend towards lukewarmers. It’s their only remaining tactic, given the way physical evidence keeps piling up.

Barry: One thing I keep reminding myself and others of is that if we think we’ll have a further warming of 8 or 9F by 2100, then that means we’ll have roughly half that by 2050. Even that much additional warming is Very Bad News.

Overall, the biggest monster under my bed is still the permafrost feedback. With a warming Arctic and the seeming determination of many governments to treat BAU as a religion, it’s only a matter of time before we unleash an immense pulse of CO2 and methane from up north. Whether that happens in 2080 or 2040 or 2020 or it’s already started is a gigantic unknown.

Another amplifying feedback: Arctic ocean currents have come a to a halt. According to the book, “Thermageddon”, cold, dense, salty water pushes down to the bottom of the ocean carrying with it a large portion of the CO2 in the atmosphere. But with the halt of the ocean currents, this is no longer taking place… at least not in the Arctic.

Rabid Doomsdayer, you can read alot about the end Permian (whatever?) extinction on the Internet… there’s a book, can’t think of the name of it. Scared the pants out of a lot of disbelievers (who became “believers”) Can’t think of the name of the book.. (stressed out–Internet library time is almost over!) Later!

Speaking of delusional, I just returned from California today. The vegetation looks WORSE than the trees and plants on the East Coast. It’s like people are walking around a cadaver pretending it doesn’t stink. I have many pictures – but just a few up on the blog for now.

If we don’t stop putting toxic emissions into the air immediately, we won’t have any hope of growing any sort of food. Fruits, seeds and nuts will be stunted and unviable.

It seems to me that if we start hearing more about ‘lukewarming’ that is good news. The deniers have been pushed from “its not happening” to “its happening but its the sun (or whatever)” to “its happening but its not that bad”. Perhaps the data will win out, but in time to make a difference?

Also the uber-rich might want to realize that if the economy collapses all their “money” will be worthless! Even gold is useless to people who want food.

I should mention, the ‘Climate sensitivity is not specific to CO2′ section isn’t quite correct because different forcings have different efficacies. I updated the advanced version of this rebuttal to clarify this point. Here’s the link if you want to do the same:http://www.skepticalscience.com/climate-sensitivity-advanced.htm

… you can read alot about the end Permian (whatever?) extinction on the Internet… there’s a book, can’t think of the name of it. Scared the pants out of a lot of disbelievers (who became “believers”) Can’t think of the name of the book.. (stressed out–Internet library time is almost over!) Later!

The interesting thing here, to me, is that there is a progression in the delayer catechism. First, it ani’t happening; second, it’s not man-made; third, it’s really not a big issue compared to other things (lomborg et. al); fourth, it will cost too much to deal with; fifth,ok, it’s happening but it’s not that bad. Along the way you’ve got your breakthroughers and other sophists.

Pretty soon, we will get the call for geo-engineering in lieu of actually doing anything.

Joe has pointed out each of these apologist strategies along the way. Too bad the folks in charge weren’t
paying attention ‘casue we’re flat out of time.

Typhoon Fanapi
Typhoon Fanapi made landfall in northern Taiwan early Sunday morning local time as a Category 3 storm with 120 mph winds. Fanapi killed three people on the island, and brought rains of up to 690 mm (27.2 inches) to mountainous regions in the interior. Fanapi is the strongest typhoon so far this year, in what has been an exceptionally quiet Western Pacific typhoon season. The previous strongest typhoon this season was Typhoon Kompasu, a low-end Category 3 storm with 115 mph winds that hit South Korea in early September. As seen on Taiwan radar, Fanapi has crossed over Taiwan and is now in the Taiwan Strait between the island and mainland China. Fanapi is expected to hit China about 150 miles east-northeast of Hong Kong on Monday, as a Category 1 typhoon.

Greg –
Thanks for the link on the Karl’s landfall at Varacruz , you asked if anyone found 8 inches of rain in 90 minutes, astounding . I did. The Mexicans were lucky, Karl’s forward speed saved them from a 10 foot scenario that Taiwan suffered through last season.

I should mention, the ‘Climate sensitivity is not specific to CO2′ section isn’t quite correct because different forcings have different efficacies. I updated the advanced version of this rebuttal to clarify this point. Here’s the link if you want to do the same:

The definition of RF from the TAR and earlier IPCC assessment reports is retained. Ramaswamy et al. (2001) define it as ‘the change in net (down minus up) irradiance (solar plus longwave; in W m^–2) at the tropopause after allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values’.

The idea here is that increased solar radiance or increases in CO2 concentration affect the balance of radiation entering/leaving the climate system — and will result in a response at the “top of the atmosphere” or – tos – which is typically taken to be at the tropopause which separates the troposphere and the stratosphere. Feedbacks are in response to this change.

Definition of Climate Sensitivity:

The long-term change in surface air temperature following a doubling of carbon dioxide (referred to as the climate sensitivity) is generally used as a benchmark to compare models.

The above definition of climate sensitivity is however for the Charney Climate Sensitivity that takes into account the fast feedbacks, e.g., water vapor, clouds, sea ice, etc., but omits the slow feedbacks associated with changes in vegitation, feedbacks due to the carbon cycle and ice sheets — the latter of which are land-based.

Definition of Efficacy:

Efficacy (E) is defined as the ratio of the climate sensitivity parameter for a given forcing agent (λi) to the climate sensitivity parameter for CO2 changes, that is, Ei = λi / λCO2 (Joshi et al., 2003; Hansen and Nazarenko, 2004). Efficacy can then be used to define an effective RF (= Ei RFi) (Joshi et al., 2003; Hansen et al., 2005). For the effective RF, the climate sensitivity parameter is independent of the mechanism, so comparing this forcing is equivalent to comparing the equilibrium global mean surface temperature change.

The efficacy primarily depends on the spatial structure of the forcings and the way they project onto the various different feedback mechanisms (Boer and Yu, 2003b). Therefore, different patterns of RF and any nonlinearities in the forcing response relationship affects the efficacy (Boer and Yu, 2003b; Joshi et al., 2003; Hansen et al., 2005; Stuber et al., 2005; Sokolov, 2006). Many of the studies presented in Figure 2.19 find that both the geographical and vertical distribution of the forcing can have the most significant effect on efficacy (in particular see Boer and Yu, 2003b; Joshi et al., 2003; Stuber et al., 2005; Sokolov, 2006)…

NOTE: calculations performed by climate models do not involve the concepts of forcing, climate sensitivity or efficacy. The calculations of climate models are themselves based up the physics. Analysis in terms of forcings, climate sensitivity and efficacy only come afterward — as a means of conceptualizing the results for the ease of our understanding.

The oceanic and terrestrial CO2 reservoirs – the ‘CO2 sinks’–
have continued to absorb more than half of the total emissions
of CO2. However the fraction of emissions absorbed by the
reservoirs has likely decreased by ~5% (from 60 to 55%) in
the past 50 years (Canadell et al. 2007). The uncertainty in
this estimate is large because of the significant background
interannual variability and because of uncertainty in CO2
emissions from land use change.

The response of the land and ocean CO2 sinks to climate
variability and recent climate change can account for the
decrease in uptake efficiency of the sinks suggested by the
observations (Le Quéré et al. 2009). A long-term decrease in
the efficiency of the land and ocean CO2 sinks would enhance
climate change via an increase in the amount of CO2 remaining
in the atmosphere. Many new studies have shown a recent
decrease in the efficiency of the oceanic carbon sink at removing
anthropogenic CO2 from the atmosphere. In the Southern Ocean,
the CO2 sink has not increased since 1981 in spite of the large
increase in atmospheric CO2 (Le Quéré et al. 2007; Metzl 2009;
Takahashi et al. 2009). The Southern Ocean trends have been
attributed to an increase in winds, itself a likely consequence of
ozone depletion (Lovenduski et al. 2008). Similarly, in the North
Atlantic, the CO2 sink decreased by ~50% since 1990 (Schuster
et al. 2009), though part of the decrease has been associated
with natural variability (Thomas et al. 2008).

Future vulnerabilities of the global CO2 sinks (ocean and
land) have not been revised since the IPCC AR4. Our current
understanding indicates that the natural CO2 sinks will decrease
in efficiency during this century, and the terrestrial sink could
even start to emit CO2 (Friedlingstein et al. 2006). The response
of the sinks to elevated CO2 and climate change is shown in
models to amplify global warming by 5-30%. The observations
available so far are insufficient to provide greater certainty, but
they do not exclude the largest global warming amplification
projected by the models (Le Quéré et al. 2009).

So the consensus would seem to be that it’s a matter of how fast and how bad, not if.

A 2008 study led by James Hansen found that climate sensitivity to “fast feedback processes” is 3°C, but when accounting for longer-term feedbacks (such as ice sheet disintegration, vegetation migration, and greenhouse gas release from soils, tundra or ocean), if atmospheric CO2 remains at the doubled level, the sensitivity increases to 6°C based on paleoclimatic (historical climate) data.

Hansen et al estimate Earth System Sensitivity (ESS – that includes slow feedbacks) over Charney Sensitivity (CS – that only includes fast feedbacks) – or ESS/CS – at 2:

Paleoclimate data permit evaluation of long-term sensitivity to specified GHG change. We assume only that, to first order, the area of ice is a function of global temperature. Plotting GHG forcing [7] from ice core data [18] against temperature shows that global climate sensitivity including the slow surface albedo feedback is 1.5°C per W/m 2 or 6°C for doubled CO2 (Fig. 2), twice as large as the Charney fastfeedback sensitivity. Note that we assume the area of ice and snow on the planet to be predominately dependent on global temperature, but some changes of regional ice sheet properties occur as part of the Earth orbital climate forcing (see Supplementary Material).

As shown in Table 1, none of these assumptions greatly changes our estimate of ESS/CSacross all of the analyses presented in this article, the smallest value of ESS/CS we obtain is 1.3, and the largest is 1.5. Our combined modelling and data approach results in a smaller response (ESS/CS~ 1.4) than has recently been estimated using palaeo data from the Last Glacial Maximum, 21,000 years ago (ESS/CS ~ 2). This is probably due to the fact that transitions from glacial to interglacial conditions in the Quaternary involve large changes in the Laurentide and Eurasian ice sheets (see, for example, ref. 36), which result in a significant large-scale albedo feedback in these regions that is irrelevant for climates warmer that present.

Either way the climate sensitivity that people have been talking about underestimates the warming that we can expect because by definition it omits the slow feedbacks — which aren’t necessarily that slow (e.g., the reduction in plant efficiency over the past decade, the saturation of some ocean CO2 sinks, Boreal forests in Canada, rising levels of methane emissions due to permafrost melt in Arctic tundra and Arctic shallow water continental shelves, e.g., near the coastline of Siberia.

Joe,
It bothers me that the various climate feedbacks – methane from permafrost and arctic shelves; warming stratified seas which reduce phytoplankton production (James Lovelock’s model); drying tropical wetlands, forests and firestorms; reducing CO2 sinks etc. all seem to be assessed in isolation. Of course, they don’t merely add, they compound by feeding on each other.

Are there any studies which attempt to pull them all together in a single (full) ocean-atmospheric global model? I haven’t seen any. It seems to me that we need an answer urgently, even a heavily-qualified, cautious one. What do the climate modellers say?

Austral, what you’re describing is a carbon cycle model, work on which is at the early stages. The recent Lunt et al. paper that Timothy mentioned is a good example, and IIRC includes a discussion of the limitations. A public copy is here.

AIUI the big step after that in model development will be to get a more realistic ocean component.

Further to Timothy’s comment, at the time the Charney committee came up with its definiation of sensitivity in the ’70s, it was assumed that the slow feedbacks would not kick in by 2100 and could therefore be excluded. Wrong, as it turns out.

JR: BTW, I believe Dr. Curry is a lukewarmer (2C increase with doubling).

As important as lukewarmers are those who state that Earth’s climate is changing, but it has changed in the past and a warmer world will have winners and losers but will be no worse overall.

I’ve been reading up on paleoclimates lately and I’ve come to realize that there is actually strong proof that for humans and mammals in general, we are already living in a world that is warmer than optimal. In other words, yes there is an optimal climate and we’re beyond that and getting worse.

It might do some good to begin pointing out specific examples and then challenge the lukewarmers to find fault.

For example the U.S. Great Basin was filled with lakes and marshes and supported many more native Americans prior to about 7,000 YBP. The Great Salt Lake was once as deep and as large as Lake Michigan, but like L. Michigan, it was sensitive to slight changes in evaporation rates and so is now largely gone.

Much of the Sahara Desert was savannah until about 5,000 YBP with ample water and supported many more people than today (obviously).

The loss of the World’s great river deltas to sea level rise will be a huge blow to humans, fish and wildlife. I will miss Louisiana and Florida.

I would bet there are many more examples where much habital land has been lost to natural and un-natural global warming. Interior Australia. The Tibetan Plateau.

Perhaps one of your blog readers who knows more about this than me could write a guest post.

Thanks for the reference Steve Bloom, (“Earth system sensitivity inferred from Pliocene modelling and data”). James Hansen is surely right to insist that paleo-data is a necessary reality-check on climate models.

However, the crucial difference here is the unprecedented speed of our current global heating – around twenty times faster than in previous deglaciations. This will affect the rate of methane production, for instance, and is surely a likely candidate for the unexplained swift response of the PETM events.
Here in Australia we have a foretaste of global heating, with new desalination plants appearing around the coastline, decade-long droughts, and dreadful firestorms. There may well be other surprises in store.

I know that fire is frightening and that many people can die. But I think the really frightening thing is the heat-related deaths apart from fire.

During our foretaste of hell a couple of years ago, more people died from heat in South Australia and Victoria than from the Black Saturday fires the following year. And Russia had many thousands die from heat this year, but the deaths in their fires were in the hundreds. I’ve not seen figures on deaths from the south Asia heatwave preceding the floods but, depressingly, it would be no surprise for me to see them exceed the deaths from drowning.

Question: If it warms 1.5C globally before 2100 will Arctic temps be 4.5C to 6C due to Arctic amplification? At that temperatures surely most of the permafrost will melt releasing large volumes of carbon/methane?

Thank you Joe for this great summary of various physical AND natural processes effecting the temperatures in the future. As we know from paleoclimate records the feedbacks for longer timeframes are larger than the immediate feedbacks. IMHO, saying the temperature rise for doubling the CO2 is 3 C, gives me a somewhat misleading thought that the doubling is done by humans, though this is how it must be said in scientific language. As the various feedbacks take different times to show their full effect, one cannot make up a linear relation which includes all the feedbacks.

When I’m thinking of the future, for me it is quite clear that fertilizing poor soils in the cooler climates is one thing that may mitigate the future warming. So are the various biochar projects. As the oceans get fertilized from the runoff via rivers, is there some way to get the phosphorus back on land, where humans live? If this goes on, the only winners of this ‘extrnalities are externalities, we don’t count them’-escapade to maximally increase the local entropy are the blue-green algae.

Planted some salads indoors a while back, partly to see how they grow during winter.

adelady – I don’t know why they persist in calling such deaths “heat related” when in actuality, they are “pollution related” because higher temperatures = higher levels of toxic ozone:

“Global Warming Will Lead to serious Health Problems”

“As global warming causes hot summer days to get hotter, concentrations of an air pollutant called ozone increase, forming lung-damaging pollution commonly known as smog.”

“Outdoor work, play, and exercise increase the amount of air pollution people inhale. In controlled clinical studies, breathing ozone has been linked to reduced pulmonary function, increased cough, and chest tightness. Reduced lung function and physical performance, increased airway reactivity, and acute inflammation have been found at exposures well below 80 parts per billion (ppb), even in healthy adults. Other health effects of ozone include an increase in hospital admissions and even premature mortality…”

“According to a recent MIT study, we’re currently on pace to reach this doubled atmospheric CO2 level by the mid-to-late 21st century.”

That would be about 800 parts per million of CO2. That is impossible. There will be no one here to observe it or act upon it.

Here is a rational response by “Beam Me Up Scotty”:

“It is appropriate to be alarmed when facing extinction.
What do I tell my grandkids?”

Bill McKibben’s comment – “This is extraordinarily useful–thanks for making all the data available in one place” is not appropriate.

McKibben’s comment is like someone on the Titanic observing: “Oh, marvelous. Thanks so much for pointing out the extraordinarily large ice berg we are about to crash into. Let’s all go up on deck and witness it!”

There are so many disconnects in this arena of global warming. They are amazing in themselves.

I’m not sure I follow you. Isn’t air pollution the least of our problems? Warming that will kill food crops is the one that will do us in.

Based on how extreme warming events so far have touched down here and there on earth (Russia’s wheat, Europe’s dying off due to heat) there will be places on earth where crops will survive for a time.

Exporting and importing of foods – for those who can afford them – will keep some people alive. But in the end there will be no safe havens for agriculture if I understand the consensus. (I realize some scientists say man will move to polar regions and be able to survive there)

Plants here on the central west coast of California seem to be healthy. After all they are getting extra CO2 which they like. Central coast is relatively pollution free, say compared to southern California.

Austral, I was thinking something similar. The rate of carbon accumulation also exceeds that leading into the PETM. So if we don’t have any evidence for a prehistoric event involving the rates we’re now pushing, I wonder if that puts some limitation on using paleoclimate data to constrain upper sensitivity estimates. If today’s oceans respond to rapid change with a relatively sudden slowing of the “biological pump” and reduction of vertical mixing etc., that along with the other feedbacks would seem to make higher figures at least possible.

#44 Wit’s End, Smog in Adelaide is not as much of a problem as it may be in other cities – 15% humidity when the air is 40+ does the trick all by itself. It takes your breath away. And many of the heat-related deaths here were literally heat. Some elderly people insist on dressing “correctly” regardless of the weather forecast, and they don’t change their drinking habits – the ‘I’ll wait till morning tea time’ approach. And of course, ingrained frugality dictates that the air conditioner only goes on for visitors.

We now have a system of Red Cross volunteers who ring people on excess heat days to remind them to drink and how to cool off and how to recognise when they should call an ambulance.

Thanks, Joe – a really excellent and clear explanation. Some of it wass a bit rough going,since I dont have much science background, but it is accessible to an intelligent, college-educated person like me.

And to #12, who says “we can adapt” under circumstances – it depends who
“we” are. Many small farmers in India plant before the monsoon and then
pray for rain. If the monsoon comes within a certain time period, then their crops will grow. If not, they wont, and many of these farmers cant afford to plant new seeds. Desperate because they have no food to feed their families, some commit suicide. So, if climate change results in monsoons that are less regular (and there is evidence
that this is already happening) some of the people who live on the edge (and there are millions of them in the Third World) will fall over the edge.

@46 William P: There is not one single problem. There are many.
1. Nutrition: Drought + Flood = less agriculture
Disturbance of ocean food chain & ocean acidification = less fish, less fishing
less glaciers = less fresh water
2. Infrastructure and housing damage: chaotic weather leads to flooding (where to build our homes safely?); more precipitation leads to more flooding; more drought leads to more wildfires;
Melting glaciers and shelf ice leads to rising sea levels; rising sea levels lead to more damage when more strong storms occur.
3. Secondary damages: Security issues due to instable countries; insurance prices; food prices; etc.

There are some positive effects as well. Like more arable land for Russia (at least that’s what they thought until this year). Or more productivity from plants (at least thats what we thought until this year.

So the effects are plenty; reducing them to food only doesn’t come close to the full extent.

Is there a place to check on “current” (2010) methane concentrations in the atmosphere. There must be some observatories that release data on a regular basis to the public. Climatedata has only graphs for 2009 Thanks in advance to someone who can help, will be greatly appreciated.

Time to build an underground bunkers in Nothern Canada with spacestatiion-type nutritional cycle?

It will not matter what is said for it will be watered down by the political part of the IPCC report. Being conservative in nature (so are the scientists) science will not promote anything but conservative projections and probabilities due to the idea of being wrong which is not only career threatening but also skeptic cheering.

3C for a pre industrial doubling of CO2 is about right. The only factor that is really a problem is the speed of our emission relative to past warming and cooling times which are a lot slower globally then our attempts now. 200 years is no time at all and that in itself may make it significantly different from previous warming episodes.

William P., air pollution is the least of our problems because the industries that create air pollution have succeeded in making the topic unfashionable, using the same tactics as the tobacco companies – funding deniers and lawsuits against the EPA, defunding research, delaying regulation.

At the top of the blog is a page titled: Basic Premise, which has a list with direct links to dozens of published, peer-reviewed scientific research that demonstrate in controlled studies the following:

1. volatile organic compounds released from burning fuel react with UV radiation and produce ozone
2. the levels of background tropospheric ozone are inexorably rising
3. ozone travels across continents and impacts rural as well as urban areas
4. ozone causes and/or aggravates human health problems including: cancer, emphysema, asthma, allergies, diabetes and death
5. vegetation is even more sensitive than humans to ozone exposure. Ozone causes the stomates of foliage to close, and also enters the tissue leading to damaged leaves and needles, with stippling, bronzing, singeing, stunted growth, reduced reproduction, and can lead to death.
6. US government estimates of crop losses due to ozone are in the billions annually
7. Trees and other plants weakened by exposure to ozone are more vulnerable to insects, disease, fungus, and severe weather – including drought and wind
8. there has been a concerted campaign funded by fossil and biofuel industry to obfuscate and dilute the science of ozone damage, just as there has been a similar effort to question the science of climate change, and had been a decades-long effort by the tobacco industry to conceal the link between smoking and fatal or chronic diseases. For example, the EPA, charged with protecting public health from pollution, has been sued numerous times to delay regulations designed to reduce the production of toxic emissions that lead to ozone.

These are all simple facts. I do realize ozone is invisible so it takes a leap of imagination to link it to cancer and tree death. Have you ever seen a germ? Do you question whether germs exist, or whether they cause disease?

I urge you to go outside and do a close-up inventory of vegetation. Pick any spot, you will find leaves are damaged on any sort of plant, and trees crowns are thin. When tree crowns are thin, the root system is even more so.

Lastly, I would add that the idea that excess CO2 is beneficial food for plants is about as sophisticated an understanding as saying that excess calories are good for people. How’s that obesity thing working out for the American public, healthwise?

I think the developing consensus is that the worst near-term threat from climate change is to agriculture. Irrigation is one factor with potential impacts that are easy to understand. If the U.S. Midwest, for example, stops getting enough rain, crops there will wither.

Temperature and CO2 level, however, are areas where more research is needed. But it’s already known that some plants do well with more CO2 and others do not. High temperatures are another limiting factor. Some crops won’t germinate when it’s too warm. This upper limit is not that high; it falls within the range of temperatures we already encounter.

Rice is a good example.

A 1975 conference on rice cultivation and climate change found general agreement that the maximum temperature for germination is in the range 40 to 45 ° C (104 to 113 °F).

– Proceedings of the Symposium on Climate & Rice, by International Rice Research Institute, 1976

Another source notes that rice plants are typically germinated in the early spring because they prefer lower temperatures at this stage. Once planted, they should have higher temperatures, above 22°C — but not too high. He gives 35°C (95°F) as the upper limit.

Concerning post #30: I’ve read that when the oceans become saturated, when they become a source of emissions rather than a sink, it’s “game over”. Sort of scarey the way Joe wrote, “the literature is now mixed on whether this is happening yet. But it is coming, yes”.

Wit’sEnd, I haven’t noticed the crowns of trees but I’ve definitely been aware of all the insect nests on trees this summer. The last few years I’ve noticed a few trees with the sacs but this summer was really awful! I felt so bad for the trees and kept wondering why foresters or government employees or SOMEBODY didn’t come out and clip the things off before they spread– and then they DID spread! Some trees were completely covered by the end of the summer and died! And they just spread from one tree to the next! What a waste! And then there were of course the Pine trees which just toppled over! Amazing! Huge trees with branches as large as elephant’s legs, just falling apart! If it’s this bad now, it’s scarey to think of what the future will be.

#57–Actually, I did go outside and do a “close up inventory of vegetation”. For some time, whenever I looked out my bedroom window, I kept thinking something was missing, things just didn’t look right; everything looked bland but I couldn’t figure out what it was. Then I went outside to feed the stray cat one day, looked down at the ground and it dawned on me! Everything was dead! Where were the bumble bees, the butterflys, grasshoppers, the praying mantis, etc. we used to see as kids? There were none! Just dry, dead dirt… and, of course, the green, man-laid carpet (grass). People use herbicides to kill dandelions and it no doubt kills a heck of a lot of other stuff as well!

Yeah! The biosphere is shrinking. Plants are at the bottom of the food chain, they are dying, and everything that feeds on them is endangered.

Insects and disease and fungus thrive in air pollution – that has been demonstrated in many scientific studies.

It’s a terribly frightening and awful subject. I just had a nightmare that some rather vicious person chopped my hands off from my wrists, to keep me from typing. It was only a dream! But evidence of how scary the prospect is, of dying vegetation. How threatening…the good news is, we COULD do something to halt it!